1. Field of the invention
The present invention relates to optical interconnects.
2. Discussion of the Background
The coupling of optical signals between components (e.g., circuit boards or other components) is an area of growing interest. Metal interconnections (e.g., metal backplanes) appear to have reached their speed limits, and therefore, optical backplanes and optical interconnect schemes are being considered as the next generation board-to-board interconnect solution. Single channel optical connections have been used for years, but the limit of pulse coded modulation (PCM) through a single optical channel is also reaching a practical limit.
To solve this problem, multiple parallel optical “paths” or “channels” are used. By paralleling paths, one can achieve higher data rates. The greater the number of paths the greater the overall throughput. In some applications, arrays of low cost lasers (e.g., a vertical cavity surface emitting laser (VCSEL)) are used for transmitting the optical signals and low cost photodiode arrays (e.g., GaAs photodiodes) are used for detecting the optical signals.
Problems exist when one is trying to interface the transmitting and detecting arrays. For example, the lasers used for transmission may emit light of 0.85 micrometers wavelength into a twenty-degree cone. The large cone angle creates cross-talk problems when attempting to couple each individual laser to an individual detector. Further, the lasers are usually situated on a recessed horizontal surface, thus emitting light into cones with vertical axes. This arrangement creates logistic problems because the light must be moved up (from a typical board) about an inch and a half followed by about two inches horizontally to an adjacent board, then down an inch and a half to the upward looking detectors.
What is desired is an optical multi-channel interconnect that provides maximum optical isolation of adjacent channels (i.e., minimum crosstalk) while also providing minimal optical signal power loss.